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CD(4) FreeBSD Kernel Interfaces Manual CD(4)
NAMEcd - SCSI CD-ROM driver
SYNOPSISdevicecdDESCRIPTION
The cd driver provides support for a SCSI CD-ROM (Compact Disc-Read Only
Memory) drive. In an attempt to look like a regular disk, the cd driver
synthesizes a partition table, with one partition covering the entire
CD-ROM. It is possible to modify this partition table using
disklabel(8), but it will only last until the CD-ROM is unmounted. In
general the interfaces are similar to those described by ada(4) and
da(4).
As the SCSI adapter is probed during boot, the SCSI bus is scanned for
devices. Any devices found which answer as CDROM (type 5) or WORM (type
4) type devices will be `attached' to the cd driver. Prior to
FreeBSD 2.1, the first device found will be attached as cd0 the next,
cd1, etc. Beginning in FreeBSD 2.1 it is possible to specify what cd
unit a device should come on line as; refer to scsi(4) for details on
kernel configuration.
The system utility disklabel(8) may be used to read the synthesized disk
label structure, which will contain correct figures for the size of the
CD-ROM should that information be required.
KERNEL CONFIGURATION
Any number of CD-ROM devices may be attached to the system regardless of
system configuration as all resources are dynamically allocated.
IOCTLS
The following ioctl(2) calls which apply to SCSI CD-ROM drives are
defined in the header files <sys/cdio.h> and <sys/disklabel.h>.
DIOCGDINFO
DIOCSDINFO (struct disklabel) Read or write the in-core copy of
the disklabel for the drive. The disklabel is
initialized with information read from the scsi
inquiry commands, and should be the same as the
information printed at boot. This structure is
defined in the header file <sys/disklabel.h>.
CDIOCPLAYTRACKS (struct ioc_play_track) Start audio playback given a
track address and length. The structure is defined
as follows:
struct ioc_play_track
{
u_char start_track;
u_char start_index;
u_char end_track;
u_char end_index;
};
CDIOCPLAYBLOCKS (struct ioc_play_blocks) Start audio playback given
a block address and length. The structure is
defined as follows:
struct ioc_play_blocks
{
int blk;
int len;
};
CDIOCPLAYMSF (struct ioc_play_msf) Start audio playback given a
`minutes-seconds-frames' address and length. The
structure is defined as follows:
struct ioc_play_msf
{
u_char start_m;
u_char start_s;
u_char start_f;
u_char end_m;
u_char end_s;
u_char end_f;
};
CDIOCREADSUBCHANNEL (struct ioc_read_subchannel) Read information from
the subchannel at the location specified by this
structure:
struct ioc_read_subchannel {
u_char address_format;
#define CD_LBA_FORMAT 1
#define CD_MSF_FORMAT 2
u_char data_format;
#define CD_SUBQ_DATA 0
#define CD_CURRENT_POSITION 1
#define CD_MEDIA_CATALOG 2
#define CD_TRACK_INFO 3
u_char track;
int data_len;
struct cd_sub_channel_info *data;
};
CDIOREADTOCHEADER (struct ioc_toc_header) Return summary information
about the table of contents for the mounted CD-ROM.
The information is returned into the following
structure:
struct ioc_toc_header {
u_short len;
u_char starting_track;
u_char ending_track;
};
CDIOREADTOCENTRYS (struct ioc_read_toc_entry) Return information from
the table of contents entries mentioned. (Yes, this
command name is misspelled.) The argument structure
is defined as follows:
struct ioc_read_toc_entry {
u_char address_format;
u_char starting_track;
u_short data_len;
struct cd_toc_entry *data;
};
The requested data is written into an area of size
data_len and pointed to by data.
CDIOCSETPATCH (struct ioc_patch) Attach various audio channels to
various output channels. The argument structure is
defined thusly:
struct ioc_patch {
u_char patch[4];
/* one for each channel */
};
CDIOCGETVOL
CDIOCSETVOL (struct ioc_vol) Get (set) information about the
volume settings of the output channels. The
argument structure is as follows:
struct ioc_vol
{
u_char vol[4];
/* one for each channel */
};
CDIOCSETMONO Patch all output channels to all source channels.
CDIOCSETSTEREO Patch left source channel to the left output channel
and the right source channel to the right output
channel.
CDIOCSETMUTE Mute output without changing the volume settings.
CDIOCSETLEFT
CDIOCSETRIGHT Attach both output channels to the left (right)
source channel.
CDIOCSETDEBUG
CDIOCCLRDEBUG Turn on (off) debugging for the appropriate device.
CDIOCPAUSE
CDIOCRESUME Pause (resume) audio play, without resetting the
location of the read-head.
CDIOCRESET Reset the drive.
CDIOCSTART
CDIOCSTOP Tell the drive to spin-up (-down) the CD-ROM.
CDIOCALLOW
CDIOCPREVENT Tell the drive to allow (prevent) manual ejection of
the CD-ROM disc. Not all drives support this
feature.
CDIOCEJECT Eject the CD-ROM.
CDIOCCLOSE Tell the drive to close its door and load the media.
Not all drives support this feature.
NOTES
When a CD-ROM is changed in a drive controlled by the cd driver, then the
act of changing the media will invalidate the disklabel and information
held within the kernel. To stop corruption, all accesses to the device
will be discarded until there are no more open file descriptors
referencing the device. During this period, all new open attempts will
be rejected. When no more open file descriptors reference the device,
the first next open will load a new set of parameters (including
disklabel) for the drive.
The audio code in the cd driver only support SCSI-2 standard audio
commands. As many CD-ROM manufacturers have not followed the standard,
there are many CD-ROM drives for which audio will not work. Some work is
planned to support some of the more common `broken' CD-ROM drives;
however, this is not yet under way.
SYSCTL VARIABLES
The following variables are available as both sysctl(8) variables and
loader(8) tunables:
kern.cam.cd.retry_count
This variable determines how many times the cd driver will retry a
READ or WRITE command. This does not affect the number of retries
used during probe time or for the cd driver dump routine. This value
currently defaults to 4.
kern.cam.cd.%d.minimum_cmd_size
The cd driver attempts to automatically determine whether the drive
it is talking to supports 6 byte or 10 byte MODE SENSE/MODE SELECT
operations. Many SCSI drives only support 6 byte commands, and ATAPI
drives only support 10 byte commands. The cd driver first attempts
to determine whether the protocol in use typically supports 6 byte
commands by issuing a CAM Path Inquiry CCB. It will then default to
6 byte or 10 byte commands as appropriate. After that, the cd driver
defaults to using 6 byte commands (assuming the protocol the drive
speaks claims to support 6 byte commands), until one fails with a
SCSI ILLEGAL REQUEST error. Then it tries the 10 byte version of the
command to see if that works instead. Users can change the default
via per-drive sysctl variables and loader tunables. Where ``%d'' is
the unit number of the drive in question. Valid minimum command
sizes are 6 and 10. Any value above 6 will be rounded to 10, and any
value below 6 will be rounded to 6.
FILES/dev/cd[0-9][a-h] raw mode CD-ROM devices
DIAGNOSTICS
None.
SEE ALSOcam(4), da(4), disklabel(8), cd(9)HISTORY
This cd driver is based upon the cd driver written by Julian Elischer,
which appeared in 386BSD-0.1. The CAM version of the cd driver was
written by Kenneth Merry and first appeared in FreeBSD 3.0.
BUGS
The names of the structures used for the third argument to ioctl() were
poorly chosen, and a number of spelling errors have survived in the names
of the ioctl() commands.
FreeBSD 11.0-PRERELEASE April 9, 2014 FreeBSD 11.0-PRERELEASE